Thermoelectric cooling and/or moderation of transient thermal load using phase change material

ABSTRACT

Techniques described and illustrated herein can permit high luminous flux and/or longer lifetimes for a class of photoemissive device configurations and/or uses that generate intense highly localized, but transient heat flux. For example, certain Light Emitting Diode (LED) applications, e.g., for flash illumination, certain solid state laser configurations and other similar configurations and uses may benefit from the developed techniques. In particular, it has been discovered that by locating an amount of appropriate phase change material in close thermal proximity to such a photoemissive device, substantial generated heat fluxes may be “absorbed” into a phase transition of the phase change material. In some configurations, a thermoelectric is employed in conjunction with the phase change material. For example, the thermoelectric may at least partially define a heat transfer path from the photoemissive device to the phase change material. Similar configurations may be employed for photosensitive devices. In such configurations, the phase change material may effectively clamp one side (typically the hot side) of the thermoelectric as heat transferred across the thermoelectric is absorbed into the transition of at least some of the phase change material from a first state thereof to a second state. The thermoelectric may be transiently operated in substantial synchrony with operation of the photoemissive or photosensitive device to provide extremely high density spot cooling when and where desired.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims benefit of U.S. Provisional Application No.60/621,382 entitled “TRANSIENT THERMOELECTRIC COOLING OF OPTOELECTRONICDEVICES,” filed on Oct. 22, 2004.

In addition, this application is related to commonly-owned U.S. patentapplication Ser. No. ______ entitled “TRANSIENT THERMOELECTRIC COOLINGOF OPTOELECTRONIC DEVICES,” and naming Uttam Ghoshal as inventor, filedon even date herewith, the entirety of which is incorporated herein byreference.

BACKGROUND

1. Field of the Invention

The present invention relates to management of transient thermal loads,such as exhibited by some optoelectronic devices, and particularly tothermoelectric cooling and/or moderation of transient thermal loadsusing phase change material.

2. Related Art

Modern digital devices including consumer electronics increasinglyemploy optoelectronic devices. Digital cameras (as well as phones thatinclude camera features) are good examples. Arrays of charge coupleddevices (CCDs) or complementary metal oxide semiconductor (CMOS) sensorsare used for image capture. In some devices, a flash may be employed,which may itself employ light emitting diodes (LEDs) or othertechnologies.

Individual elements of a CCD array convert energy from incoming lightinto electrons. The higher the intensity of incoming light (or thelonger an element is exposed), the more free electrons an elementaccumulates. Of course, like most sensors, CCD's (and CMOS devices) aresusceptible to noise because the materials and device structures exhibita baseline level of electron “action” (or current). In sensors, thiscurrent is usually called dark current (the “dark” in the name impliesthat the current was formed without exposure to light). Dark currentincreases with temperature.

Sensitivity is typically limited by background noise. In general,smaller elements must tolerate higher noise for a given level ofsensitivity. Accordingly, as higher and higher pixel densities aresupported (often with smaller and smaller sensor elements), sensitivityand noise issues may become increasingly important. Efficient techniquesfor cooling arrays of optoelectronic sensors are therefore desired.

In addition to photosensitive devices, some photoemissive devicesexhibit temperature sensitivity. For example, luminous flux and lifetimeof white flash LEDs can be affected by operating temperatures. Mostapproaches to cooling flash LEDs and CCD have been limited to passiveheat spreading packages. Unfortunately, it is difficult to increase theperformance of white LEDs and CCDs with known passive methods.Alternative techniques are desired.

SUMMARY

The invented techniques described and illustrated herein can permit highluminous flux and/or longer lifetimes for a class of photoemissivedevice configurations and/or uses that generate intense highlylocalized, but transient heat flux. For example, certain Light EmittingDiode (LED) applications, e.g., for flash illumination, certain solidstate laser configurations and other similar configurations and uses maybenefit from the developed techniques. In particular, it has beendiscovered that by locating an amount of appropriate phase changematerial in close thermal proximity to such a photoemissive device,substantial generated heat fluxes may be “absorbed” into a phasetransition of the phase change material.

Although particular phase change materials and particular phasetransitions can vary from exploitation to exploitation, solid-liquidphase transitions exhibited in low-melt point solders or galliumconfined in a nickel cavity are typically suitable for many of theoptoelectronic device cooling implementations described herein. Moregenerally, other endothermic phase transitions (whether solid-liquid,liquid-gas, solid-gas or solid-solid) of other materials may beexploited as long as transition temperatures, latent heats of transitionand thermal conductivities of the materials are suitable for the heatfluxes involved and suitable material confinement/compatibilitytechniques are available.

In some configurations, a thermoelectric is employed in conjunction withthe phase change material. For example, the thermoelectric may at leastpartially define a heat transfer path from the photoemissive device tothe phase change material. Similar configurations may be employed forphotosensitive devices. In such configurations, the phase changematerial may effectively clamp one side (typically the hot side) of thethermoelectric as heat transferred across the thermoelectric is absorbedinto the transition of at least some of the phase change material from afirst state thereof to a second state. The thermoelectric may betransiently operated in substantial synchrony with operation of thephotoemissive or photosensitive device to provide extremely high densityspot cooling when and where desired.

Alternatively (or additionally), phase change material may be disposedin close thermal proximity to the photoemissive device, absorbingsubstantial transient heat flux into the transition of at least some ofthe phase change material from a first state thereof to a second state.In this way, a phase change material (and an appropriate amount thereof)can be selected to absorb the transient heat flux generated or evolvedby the photoemissive device, thereby avoiding large localized excursionsin temperature of the device that may otherwise occur when the heat fluxgenerated or evolved overwhelms conventional heat transfer pathways awayfrom the photoemissive device. In some such configurations, the phasechange material may be employed with a thermoelectric (e.g., between thephotoemissive device and the thermoelectric). In some configurations,phase change material may be employed without a thermoelectric simply tomoderate thermal transients generated by photoemissive device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1A depicts an illustrative configuration that includes both aphotosensitive device and a photoemissive device, either or both ofwhich may employ a body of phase change material in accordance with someembodiments of the present invention.

FIGS. 1B and 1C depict respective synchronization configurations thatmay be employed in conjunction with some device configurations thatemploy phase change material in accordance with embodiments of thepresent invention. In particular, FIGS. 1B and 1C depict respectivesynchronization configurations in which one or more synchronizationcircuits optionally coordinate readout or excitation of thephotosensitive and photoemissive devices with operation of respectivethermoelectric coolers.

FIG. 2 depicts an illustrative photoemissive device configuration inwhich a body of phase change material is employed in accordance withsome embodiments of the present invention to clamp the hot sidetemperature of a thermoelectric.

FIG. 3 depicts related current and temperature profiles in anillustrative photoemissive device configuration, such as thatillustrated in FIG. 2, in which a body of phase change material isemployed in accordance with some embodiments of the present invention toclamp the hot side temperature of a thermoelectric.

FIG. 4 depicts an illustrative photosensitive device configuration inwhich a body of phase change material is employed in accordance withsome embodiments of the present invention to clamp the hot sidetemperature of a thermoelectric.

FIG. 5 depicts an illustrative photoemissive device configuration inwhich a body of phase change material is employed in accordance withsome embodiments of the present invention to absorb heat evolved by aphotoemissive device during transient operation thereof and in which athermoelectric is employed to cool the body of phase change material.

FIG. 6 depicts related current and temperature profiles in anillustrative photoemissive device configuration, such as thatillustrated in FIG. 5, in which a body of phase change material isemployed in accordance with some embodiments of the present invention toabsorb heat evolved by a photoemissive device during transient operationthereof.

FIG. 7 depicts related current and temperature profiles in anillustrative photoemissive device configuration, such as thatillustrated in FIG. 5, in which a body of phase change material isemployed in accordance with some embodiments of the present invention toabsorb heat evolved by a photoemissive device during transient operationthereof.

FIG. 8 depicts an illustrative photoemissive device configuration inwhich a body of phase change material is employed in accordance withsome embodiments of the present invention to absorb heat evolved by aphotoemissive device during transient operation thereof and therebymoderate temperature of the photoemissive device.

FIG. 9 depicts an illustrative cooling configuration for a photoemissivedevice employing a thermoelectric cooler and a body of phase changematerial.

FIG. 10 depicts an illustrative cooling configuration for aphotoemissive device employing a thermoelectric cooler and a body ofphase change material.

FIGS. 11A-11E show an embodiment of a module containing a body of phasechange material in various stages of construction.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

While not limited thereto, the invented techniques described andillustrated herein can permit high luminous flux and greater lifetimesfor flash LEDs, and greater photon sensitivity and lower dark currentsfor CCD/CMOS imagers. Accordingly, we describe aspects of the inventiveconcepts in the context of configurations, optoelectronic devices,materials and heat fluxes typical of consumer electronics such asdigital cameras and mobile phones that incorporate similar technologies.However, as more completely described herein, the invention is notlimited to such exploitations.

In particular, the description that follows emphasizes exploitations ofthe present invention in which a light emitting diode, e.g., a whiteLED, or other photoemissive device is used in a flash mode of operation,e.g., as flash illumination to support digital imaging. In suchexploitations, extremely high transient thermal flux can be generated.Particularly for white LEDs, quality of the luminance, includingintensity and in some cases spectral characteristics may be affected byoperating temperature of the LED. Furthermore, useful operating life ofsuch LEDs can be adversely affected by operation at high temperatures.In addition, in typical exploitations for small form factor electronics,such as digital cameras, phones, etc., thermal sensitivity of otheroptoelectronic devices, e.g., CCD or CMOS imagers, RF electronics, etcmay be adversely affected by thermal issues related to operation of suchan LED.

Sensitivity and therefore performance of certain photosensitive devicessuch as CCD or CMOS imagers is typically limited by thermal backgroundnoise. In general, smaller or faster responding elements must toleratehigher levels of noise for a given level of sensitivity. Accordingly, ashigher and higher pixel densities are supported (often with smaller andsmaller sensor elements), sensitivity and noise issues becomeincreasingly important. Efficient techniques for cooling arrays ofoptoelectronic sensors are desirable. Since many CCD or CMOS imagers(e.g., those employed for image capture) are operated intermittently,rather than continuously, transiently applied cooling power can beadvantageously employed as described herein.

For these and other reasons, cooling of a white LED flash illuminator toovercome a transient thermal load (or moderation thereof) and/ortransient cooling of a CCD or CMOS imager serve as a useful descriptivecontext for certain inventive concepts and designs. However, based onthe description persons of ordinary skill in the art will appreciateother exploitations of the described techniques. Accordingly, withoutlimitation on the scope of inventive concepts described and claimedherein, we now describe certain exemplary embodiments.

General Techniques

In some, though not all, embodiments in accordance with the presentinvention, we exploit two basic technologies. First, we use transientcooling properties of thermoelectric coolers to get large cooling powersand temperature differentials. For example, in some embodiments, athermoelectric cooler for an illuminator or imager is operated in agenerally synchronous manner with flash illumination or image capture.Peltier cooling provided by a typical thermoelectric cooler is nearlyinstantaneous, but evolution of Joule heat and its subsequent back flowto a cold end of the thermoelectric element is comparatively slow. As aresult, the cooling power transiently delivered can be much higher thansteady-state performance would suggest.

Thermoelectric devices and materials are well-known in the art and awide variety of configurations, systems and exploitations thereof willbe appreciated by those skilled in the art. In general, exploitationsinclude those in which a temperature difference is developed as aconsequence of a current or electromotive force (typically voltage)across an appropriate material, material interface or quantum structure.Often, such exploitations operate based on the Peltier effect. Peltiereffects arise at interfaces between dissimilar conductive (orsemiconductive) materials. However, more generally, other effects oractions may be similarly exploited, including related or similar effects(e.g., Thomson, quantum tunneling and thermoionic effects) in materials,at material interfaces or as a result of quantum scale confinement.

Accordingly, for purposes of the present description, the term“thermoelectric cooler” is meant in the broadest sense of the term inwhich current or electromotive force is traded for temperaturedifference across a thermoelectric module, couple, element, device,material etc, and therefore includes those thermoelectric coolerconfigurations which exploit Peltier effects, as well as those thatoperate based upon Thomson, quantum tunneling, thermoionic or othersimilar effect or combination of effects. That said, for clarity ofdescription, we focus on Peltier-type thermoelectric coolers; however,based on such description, persons of ordinary skill in the art willappreciate applications of the described inventive concepts to devicesand configurations in which other thermoelectric-type effects areemployed.

Second, we employ a phase-change material. Phase-change material may bepositioned at either the hot-end or the cooled-end (or both the hot-endand the cooled-end) of a thermoelectric module, couple, element, device,material etc. When positioned at the hot-end, the phase-change materialeffectively clamps the hot side temperature of the thermoelectric asheat transferred across the thermoelectric is absorbed into thetransition of at least some of the phase change material from a firststate thereof to a second state. Because the thermoelectric nearlyinstantaneously develops a temperature differential between cooled andhot sides thereof, if the particular phase change material and amountsthereof are appropriately selected in relation to operating temperaturesand expected thermal flux, virtually all of the temperature change willbe delivered as cold-side cooling. Typically, the thermoelectric istransiently operated in substantial synchrony with operation of thephotoemissive or photosensitive device to provide extremely high densityspot cooling when and where desired.

When positioned at the cooled-end (i.e., when positioned thermallybetween the photoemissive device and the thermoelectric), thephase-change material can effectively absorb a large transient heat fluxgenerated or evolved by a photoemissive device, thereby avoiding largelocalized excursions in temperature of the device that may otherwiseoccur when the heat flux generated or evolved overwhelms a conventionalheat transfer pathway away from the photoemissive device. Thethermoelectric then acts as part of a heat transfer pathway away fromthe phase-change material, eventually reversing the phase change intowhich the large transient heat flux was absorbed. Because of the largeheat capacity represented by a phase change, the thermoelectric need notbe operated simultaneously (in a transient mode) with operation of thephotoemissive device. Rather, the thermoelectric may be operatedcontinuously or semicontinuously, e.g., at low power levels.Alternatively the thermoelectric may be operated intermittently at timesthat need not precisely correspond to operation of the photoemissivedevice. In this way, peak power requirements may be reduced for a systemthat includes both the thermoelectric and the photoemissive device.

In general, a thermoelectric cooler may be advantageously employed whenthe heat rejection thermal resistance (R_(th)) of the cooled device(e.g., an optoelectronic device alone or in combination with anattendant body of phase change material) is less than the product of thethermodynamic efficiency of the cooler (ε) and the operating temperature(T_(g)) of the optoelectronic device divided by the total powerdissipation of the optoelectronic device (Q). In the case of acontinuously operated thermoelectric cooler, this relation can beexpressed as:R _(th) <εT _(s) /Q  (1)

For example, if ε=0.1 for thermoelectric devices with ZT=1, T_(s)=330K(57° C.), and Q=1W, then thermoelectric cooling delivered by continuousoperation of the thermoelectric will be beneficial if R_(th)<33 K/W.

In general, depending on the phase change material employed and onambient conditions, embodiments that place phase change material at (inthermal communication with) a cooled-end of a thermoelectric may operateto restore the phase change material to a phase compatible with ambientconditions or may operate to pre-transition the phase change material toan appropriate phase state. For example, in some embodiments, athermoelectric may operate to return (post photoemission) a liquid-phasephase change material to an ambient-stable, solid state. Furthermore, insome embodiments, a thermoelectric may operate to presolidify (prior tophotoemission) an ambient-stable liquid-phase phase change material. Inshort, both post-chill and pre-chill realizations are possible.

Of course, in some exploitations, thermally decoupled amounts ofphase-change material may be positioned at both ends of athermoelectric, if desired. Similarly, a thermoelectric may be omittedin certain configurations wherein the large transient heat fluxgenerated or evolved by a photoemissive device and absorbed by thephase-change material may be effectively dissipated using other activeor passive mechanisms sufficient to reverse the phase-change prior to anext operation of the photoemissive device.

Although particular phase change materials and particular phasetransitions can vary from exploitation to exploitation, solid-liquidphase transitions exhibited in low-melt point solders or galliumconfined in a nickel cavity are typically suitable for many of theoptoelectronic device cooling implementations described herein. In someembodiments, the phase-change material may include a dielectric thermalinterface material. More generally, an endothermic phase transition(whether solid-liquid, liquid-gas, solid-gas or solid-solid) of othermaterials may be exploited as long as transition temperatures, latentheats of transition and thermal conductivities of the materials aresuitable for the heat fluxes involved and suitable materialconfinement/compatibility techniques are available.

EXEMPLARY EMBODIMENTS

FIG. 1A depicts an illustrative configuration that includes twooptoelectronic devices, a photosensitive device and a photoemissivedevice, either or both of which may employ a body of phase changematerial (PCM) in accordance with some embodiments of the presentinvention. As indicated by the arrows, photons pass through a screen 8in the photosensitive device package 12 to impinge on a sensor device16. The sensor device 16 is thermally coupled to the cold end of athermoelectric cooler 40. The hot end of the thermoelectric cooler 40may be coupled to a heat dissipating device (not shown) or mounted onthe back plane 18 of the photosensitive device 10 as shown in theexample. Electrical leads 14 provide a current path between the sensordevice 16 and the back plane 18. The photosensitive device package 12 isthen mounted on a printed wiring board 30. Although depicted as makingcontact to the back plane 18, electrical leads 14 may be wire bonded,flip-chip bonded, or surface mounted directly to the printed wiringboard 30.

The photoemissive device 20 may be mounted on a separate board, or onthe same printed wiring board 30, as shown in FIG. 1A. As indicated bythe direction of the arrows emanating from the photoemissive device 20,photons are emitted through a transparent case 22 by the LED 26.Electrical leads 24 provide a current path between the LED 26 and asynchronization circuit. Although depicted as making contact to anintermediate plane, electrical leads 24 may be wire bonded, flip-chipbonded, or surface mounted directly to the printed wiring board 30. Thebase 28 of the LED 26 is thermally coupled to the cold end of a secondthermoelectric cooler 42 The hot end of the second thermoelectric cooler42 is thermally coupled to a phase change material 50, in this exampleby being thermally coupled to an encapsulant 52 confining the phasechange material 50. Alternatively, the phase change material 50 could beconfined by forming a region in which the surface tension of the phasechange material 50 inhibits its flow when it is in a liquid state.

FIGS. 1B and 1C depict respective synchronization configurations thatmay be employed in conjunction with some device configurations thatemploy phase change material in accordance with embodiments of thepresent invention. In particular, FIGS. 1B and 1C depict respectivesynchronization configurations in which one or more synchronizationcircuits optionally coordinate readout or excitation of thephotosensitive and photoemissive devices with operation of respectivethermoelectric coolers. As shown in FIG. 1B, the photosensitive device10, e.g., a CCD or CMOS array, and the first thermoelectric cooler 40are driven by a first synchronization circuit 32, while thephotoemissive device 20 and the second thermoelectric cooler 42 aredriven by a separate synchronization circuit 34. Alternatively, as shownin FIG. 1C, the photosensitive device 10 and the first thermoelectriccooler 40 may be driven by the same synchronization circuit 36 as thephotoemissive device 20 and the second thermoelectric cooler 42. As willbe discussed in more detail below with reference to FIG. 3, thesynchronization circuits 32, 34, and 36, may drive their respectivedevices substantially simultaneously or in other phase relationships.

In general, any of a wide variety of synchronization circuits ormechanisms may be employed. Suitable realizations of suchsynchronization circuits or mechanisms are typicallyapplication-specific and may constitute a matter of design choice.Indeed, suitable realizations of such synchronization circuits ormechanisms range from the sophisticated to the trivial. For example,many digital imaging exploitations in accordance with the presentinvention(s) may opportunistically exploit sophisticated programmabletiming control facilities that may already be available to support thefor the significantly more demanding timing requirements of shuttercontrol, imager travel, auto focus processing, flash synchronization,etc. Alternatively, in some realizations, suitable synchronization maybe provided simply as a byproduct of series or parallel coupling ofcurrent supply leads or paths for thermoelectric current and targetdevice (e.g., LED) excitation. Based on the description herein and thedesign alternatives available to a given exploitation, persons ofordinary skill in the art will appreciate suitable synchronizationcircuits or mechanisms.

In general, selection of appropriate target devices (e.g., LEDs),associated driver circuits, package configurations etc. are matters ofdesign choice and subject to numerous application-specific constraintsand/or figures of merit that are largely independent of thethermoelectric and/or phase change material design factors describedherein. Nonetheless, based on the description herein, persons ofordinary skill in the art will appreciate suitable selections and/oradaptations of their own configurations, parts or assemblies or thosecommercially-available now or in the future, to exploit techniques ofthe present invention. In this regard, LEDs available from variouscommercial sources, including Lumileds Lighting, U.S. LLC and Cree,Inc., are suitable for many exploitations. In general, devices and/orconfigurations that provide or allow a low thermal impedance path to athermoelectric and/or phase change material are desirable. UnpackagedLED device or wafer configurations can offer flexibility in thermaldesign, though at the potential expense of additional packaging and teststeps that could be avoided with use of a suitable packaged component.Selections of driver circuits may vary depending on a particular deviceselected.

Of course, commercial requirements and therefore suitable deviceselections are application-specific and may vary depending on theparticular commercial exploitation. As a result, a person of skill inthe art will typically consult manufacturer or supplier specificationsor recommendations. In this regard, as of the filing date of thisapplication, Lumileds Lighting, U.S. LLC provides (on it's website,www.lumileds.com) datasheets, reference design information andapplication briefs (including driver integrated circuit recommendations)and Cree, Inc. provides (on it's website, www.cree.com) specificationsand application notes (including die attach recommendations) for theirrespective products.

FIG. 2 depicts an illustrative photoemissive device configuration inwhich a body of phase change material is employed in accordance withsome embodiments of the present invention to clamp the hot sidetemperature of a thermoelectric. Photons are emitted through atransparent case 22 by the LED 26. The transparent case 22 acts as alens for the LED 26, providing a focusing function for the emittedlight. While depicted as a traditional lens, it may also be a Fresnellens, particularly when a flat, low-profile lens is desired. The base 28of the LED 26 is thermally coupled to the cold end of a thermoelectriccooler 42. The hot end of the thermoelectric cooler 42 is thermallycoupled to an encapsulant 52 confining a phase change material 50.Electrical leads 24 provide a current path between the LED 26 and asynchronization circuit. Although depicted as making contact to anintermediate plane, electrical leads 24 may be wire bonded, flip-chipbonded, or surface mounted directly to the printed wiring board 30. Whenthe LED 26 emits light, heat is generated near the LED 26 by twomechanisms. First, current flowing through the LED 26 heats the deviceby Joule heating. Second, some photons are reflected by the transparentcase 22, returning their energy to the LED 26 as heat in a processanalogous to the greenhouse effect. This heat evolved by the operationof the photoemissive device 20 may degrade the future performance of thedevice if left unchecked. In this configuration, the thermoelectriccooler 42 defines part of a heat transfer path away from thephotoemissive device 20. A substantial amount of the heat evolved duringthe transient operation of the photoemissive device 20 flows through thethermoelectric cooler 42 and into the phase change material 50 where itis absorbed. The operation of the cooling system to respond to thistransient thermal load is now described with reference to FIG. 3.

FIG. 3 depicts related current and temperature profiles in anillustrative photoemissive device configuration, such as thatillustrated in FIG. 2, in which a body of phase change material isemployed in accordance with some embodiments of the present invention toclamp the hot side temperature of a thermoelectric device. The uppergraph of FIG. 3 shows the temporal variation of current through thephotoemissive device 20 and the thermoelectric cooler 42 of FIG. 2,while the lower graph shows the associated temperature variations in thesystem. A current pulse 60 is sent to the thermoelectric cooler 42 todevelop a temperature differential between its hot and cold ends.Referring to the lower graph, the solid line shows that the temperature66 of the cold end of the thermoelectric cooler 42 diverges from thetemperature 68 of the hot end. When the temperature of the hot endreaches the phase transition temperature of the phase change material 50(T_(PHASE CHANGE)), the phase change material 50 begins to undergo aphase transition from a first phase to a second phase. During this phasetransition any heat absorbed by the phase change material 50, forexample, heat transferred to it by thermal coupling to the hot end ofthe thermoelectric cooler 42 or evolved by the operation of thephotoemissive device 20, acts only to change the phase of the material.There can be no temperature rise of the phase change material 50 aboveits phase transition temperature until all of the material has completedthe transition. As seen in the graph, this effectively clamps thetemperature of the hot end of the thermoelectric cooler 42 atT_(PHASE CHANGE). Current continues to flow in the thermoelectric cooler42, however, developing a greater temperature differential between thehot and cold ends of the device until the maximum temperaturedifferential of the thermoelectric cooler 42, ΔT_(MAX), is reached. Withthe temperature of the hot end clamped at T_(PHASE CHANGE), thetemperature of the cold end is reduced to T_(MIN), below the ambienttemperature.

Referring to the upper graph of FIG. 3, a second current pulse 62 issent to the LED 26 to stimulate the emission of light (arrow 64 in thelower graph) at approximately the same time that the temperature of thecold end of the thermoelectric cooler 42 reaches T_(MIN). As describedabove, the emission of light from the LED 26 evolves heat, which istransferred to the thermoelectric cooler 42, whose cold end is thermallycoupled to the LED 26. This begins to raise the temperature of the coldend. When the first current pulse 60 to the thermoelectric cooler 42stops, the temperature differential between its hot and cold ends fallsas the temperature of the cold end rises as heat flows toward it fromthe hot end, which is still thermally coupled to the phase changematerial 50 at T_(PHASE CHANGE). The lower graph shows that, as thesystem equilibrates, the temperature differential between the hot andcold ends of thermoelectric cooler 42 returns to zero, in this examplewhen both ends reach T_(PHASE CHANGE). At this point, no further heat isavailable to the phase change material 50 to continue its phasetransition, which then stops. Both the phase change material 50 and thethermoelectric cooler 42 are at an elevated temperature relative totheir surroundings, so heat continues to be transferred away from them.This reverses the phase transition. The reverse phase transition evolvesheat, which is transferred away toward the lower-temperature parts ofthe system, clamping the temperature of the phase change material 50(and so of the thermoelectric cooler 42) at T_(PHASE CHANGE) until thereverse phase transition is complete, returning the phase changematerial 50 to its original phase. After the reverse phase transition iscomplete, the temperature of the phase change material 50 (and so of thethermoelectric cooler 42) can fall below T_(PHASE CHANGE), and thesystem continues to cool to its equilibrium temperature. The process canthen be repeated as desired.

FIG. 4 depicts an illustrative photosensitive device configuration inwhich a body of phase change material is employed in accordance withsome embodiments of the present invention to clamp the hot sidetemperature of a thermoelectric device. Photons pass through a screen 8in the photosensitive device package 12 to impinge on a sensor device16. Electrical leads 14 provide a current path between the sensor device16 and the package 12. Although depicted as making contact to the backplane 18, electrical leads 14 may be wire bonded, flip-chip bonded, orsurface mounted directly to the printed wiring board 30. The sensordevice 16 is thermally coupled to the cold end of a thermoelectriccooler 40. The hot end of the thermoelectric cooler 40 is thermallycoupled to an encapsulant 72 confining a phase change material 70. Inthis configuration, heat flows away from the optoelectronic device atleast partially along a path defined by the thermoelectric cooler 40.Heat flows from the optoelectronic device through the thermoelectriccooler 40 to the phase change material 70, where a substantial amount ofit is absorbed. The phase change material 70 clamps the temperature ofthe hot end of the thermoelectric cooler 40 at the phase transitiontemperature of the phase change material 70 as described above withreference to FIG. 3. Thus most of the temperature differential developedacross the thermoelectric cooler 40 during operation will appear as areduction in the temperature of the cold end of the thermoelectriccooler 40, which is thermally coupled to the sensor device 16.

FIG. 5 depicts an illustrative photoemissive device configuration inwhich a body of phase change material is employed in accordance withsome embodiments of the present invention to absorb heat evolved by aphotoemissive device during transient operation thereof and in which athermoelectric is employed to cool the body of phase change material.Photons are emitted through a transparent case 22 by the LED 26. Thebase 28 of the LED 26 is thermally coupled to an encapsulant 52confining a phase change material 50, which is in turn thermally coupledto the cold end of a thermoelectric cooler 42. The hot end of thethermoelectric cooler 42 may be coupled to a heat dissipating device(not shown) or may transfer heat directly to its surroundings.Electrical leads 24 provide a current path between the LED 26 and asynchronization circuit. Although depicted as making contact to anintermediate plane, electrical leads 24 may be wire bonded, flip-chipbonded, or surface mounted directly to the printed wiring board 30. Whenthe LED 26 emits light, heat is generated near the LED 26 as explainedabove with reference to FIG. 2. In this configuration, thethermoelectric cooler 42 defines part of a heat transfer path away fromthe phase change material 50. A substantial amount of the heat evolvedduring the transient operation of the photoemissive device 20 flowsthrough the phase change material 50 where it is absorbed. As thetransient heat load is removed, heat flows from the phase changematerial 50 into the thermoelectric cooler 42. The operation of thecooling system to respond to this transient thermal load is nowdescribed with reference to FIG. 6.

FIG. 6 depicts related current and temperature profiles in anillustrative photoemissive device configuration, such as thatillustrated in FIG. 5, in which a body of phase change material isemployed in accordance with some embodiments of the present invention toabsorb heat evolved by a photoemissive device during transient operationthereof. The upper graph of FIG. 6 shows the temporal variation ofcurrent through the photoemissive device 20 and the thermoelectriccooler 42 of FIG. 5, while the lower graph shows the associatedtemperature variations in the system. A current pulse 62 is sent to theLED 26 to stimulate the emission of light (arrow 64 in the lower graph).The heat evolved during the operation of the LED 26 causes thetemperature of the phase change material 50 to rise. As described abovewith reference to FIG. 3, when the temperature of the phase changematerial 50 reaches its phase transition temperature (T_(PHASE CHANGE)),the phase change material 50 begins to undergo a phase transition from afirst phase to a second phase. At approximately the same time as the LED26 flashes, a second current pulse 60 is sent to the thermoelectriccooler 42 to develop a temperature differential between its hot and coldends. Referring to the lower graph, the solid line shows that thetemperature 66 of the cold end of the thermoelectric cooler 42 divergesfrom the temperature 68 of the hot end. The temperature of the end ofthe thermoelectric cooler 42 thermally coupled to the phase changematerial 50, in this case the cold end, is clamped at T_(PHASE CHANGE)until the phase transition is complete, so most of the temperaturedifferential developed across the thermoelectric cooler 42 duringoperation will appear as an increase in the temperature of the hot endof the thermoelectric cooler 42. Current continues to flow in thethermoelectric cooler 42, absorbing heat at the cold end and so from thephase change material 50. The endothermic phase transition stops and, asthe operation of the thermoelectric cooler 42 transfers heat away fromthe phase change material 50, the phase transition reverses, evolvingheat which is transferred to the thermoelectric cooler 42 through itscold end. After the reverse phase transition is complete, thetemperature of the phase change material 50 (and so of the cold end ofthe thermoelectric cooler 42) can fall below T_(PHASE CHANGE). With thetemperature of the cold end of the thermoelectric cooler 42 no longerclamped and current flowing through the thermoelectric cooler 42, thefull temperature differential between the hot and cold ends of thethermoelectric cooler 42 develops and the temperature of the cold enddrops below ambient temperature. When the current pulse 60 to thethermoelectric cooler 42 stops, the temperature differential between itshot and cold ends falls, as the hot end cools and the temperature of thecold end rises to ambient temperature. After the system has returned toequilibrium, the process can be repeated.

FIG. 7 depicts related current and temperature profiles in anotherillustrative photoemissive device configuration, such as thatillustrated in FIG. 5, in which a body of phase change material isemployed in accordance with some embodiments of the present invention toabsorb heat evolved by a photoemissive device during transient operationthereof. The upper graph of FIG. 7 shows the temporal variation ofcurrent through the photoemissive device 20 and the thermoelectriccooler 42 of FIG. 5, while the lower graph shows the associatedtemperature variations in the system. In this configuration, the ambienttemperature is generally above the phase transition temperature(T_(PHASE CHANGE)) of the phase change material 50, so when the flashrequest is received, a current pulse 60 is sent to the thermoelectriccooler 42 to develop a temperature differential between its hot and coldends to pre-chill phase change material 50 in anticipation of theoperation of the photoemissive device (20 in FIG. 5). Referring to thelower graph, the solid line shows that the temperature 66 of the coldend of the thermoelectric cooler 42 diverges from the temperature 68 ofthe hot end. The temperature of the end of the thermoelectric cooler 42thermally coupled to the phase change material 50, in this case the coldend, is clamped at T_(PHASE CHANGE) until the phase transition iscomplete. Current continues to flow in the thermoelectric cooler 42,absorbing heat at the cold end and so from the phase change material 50.When the cold end of the thermoelectric cooler 42 reaches the desiredtemperature, the current to the thermoelectric cooler 42 ceases and thetemperature of the hot end of the thermoelectric cooler 42 begins tofall until it reaches the ambient temperature of the system. Atapproximately the same time, a current pulse 62 is sent to the LED 26 tostimulate the emission of light (arrow 64 in the lower graph). The heatevolved during the operation of the LED 26 is absorbed by the phasechange material 50 causing its temperature to rise, first to its phasetransition temperature and then, after completion of its endothermicphase transition, to the ambient temperature of the system. Thetemperature of the cold end of the thermoelectric cooler 42 tracks thatof the phase change material 50, eventually returning to system ambient.The sequence may be repeated when the next flash request is received.

FIG. 8 depicts an illustrative photoemissive device configuration inwhich a body of phase change material is employed in accordance withsome embodiments of the present invention to absorb heat evolved by aphotoemissive device during transient operation thereof and therebymoderate the temperature of the photoemissive device. Photons areemitted through a transparent case 82 by the laser diode 86. Electricalleads 84 provide a current path between the laser diode 86 and asynchronization circuit. Although depicted as making contact to anintermediate plane, electrical leads 84 may be wire bonded, flip-chipbonded, or surface mounted directly to the printed wiring board 30. Thebase 88 of the laser diode 86 is thermally proximate to a phase changematerial 90, for example by being thermally coupled to an encapsulant 92confining the phase change material 90. When the laser diode 86 emitslight, heat is generated near the laser diode 86 as explained above withreference to FIGS. 2 and 5. The heat evolved during the operation of thelaser diode 86 causes the temperature of the phase change material 90 torise. As described above with reference to FIGS. 3 and 6, when thetemperature of the phase change material 90 reaches its phase transitiontemperature (T_(PHASE CHANGE)), the phase change material 90 begins toundergo a phase transition from a first phase to a second phase. Untilthe phase transition is complete, the temperature of the laser diode 86is clamped at T_(PHASE CHANGE). As soon as the laser diode 86 stopsemitting, no more heat is evolved and the phase transition slows andstops. The temperature of the phase change material 90 and the laserdiode 86 thermally coupled thereto is elevated with respect to thesurroundings, so heat is transferred away from the phase change material90 until the reverse phase transition is initiated. Heat continues to betransferred away from the phase change material 90 until the reversephase transition is completed, and the temperature of the phase changematerial 90, and so of the laser diode 86 thermally coupled thereto,returns to its equilibrium value, or ambient temperature.

FIGS. 9 and 10 depict illustrative arrangements of thermoelectriccoolers, phase change materials, and photoemissive devices. In FIG. 9, aphase change material (PCM) module 100 is formed by etching pits in asubstrate 102, filling the pits (typically under vacuum to avoidinclusions) with the phase change material 104, and encapsulating thephase change material by depositing a layer of metal 106. Other suitableencapsulants include polytetrafluoroethylene (PTFE, marketed as Teflon®by DuPont, Wilmington, Del.) and related polymers, parylene, or layeredstructures of parylene and aerogel. “Tarylene” is a generic term for aseries of polymers based on para-xylylene and its substitutedderivatives. Parylene N, or poly(para-xylylene), has a relatively highermelting point than parylene C, or poly(monochloro-para-xylylene), andparylene D, or poly(dichloro-para-xylylene). Parylene F, also calledparylene AF-4, is poly(tetrafluoro-para-xylylene), and has a lowerdielectric constant and higher thermal stability than parylene N. Ingeneral, such encapsulants can be employed, in configurations such asillustrated in FIG. 10, to provide thermal isolation and encapsulationthat is tolerant to expansion (and contraction) of an encapsulated phasechange material.

Referring to FIG. 9, the PCM module 100 is then bonded to the back side132 of a thermoelectric cooler (TEC) assembly 120, making thermalcontact to the hot side 126 of the TEC 122 via a thermally conductingplug 128 that passes through a layer of thermal insulation 130. Aphotoemissive device 20 is mounted on a thermally conducting pad 124that is thermally coupled to the cold end of the TEC 122, shown here asa lateral thermoelectric cooler.

FIG. 10 shows a configuration in which a PCM module is in thermalcontact with the cold end of the thermoelectric cooler. The PCM module200 is formed by etching pits in a substrate 102, filling the pits withthe phase change material 104, and encapsulating the phase changematerial by depositing a layer 208 of thermally insulating material, forexample, PTFE, parylene, or layered structures of parylene and aerogel.A bonding layer 206 of metal is deposited on top of the thermalinsulation. A layer 232 of metal is deposited on the back side of asecond substrate 234 whose front side makes thermal contact to the hotside 126 of a TEC 122 via a thermally conducting plug 128 that passesthrough a layer of thermal insulation 130. The cold end of the TEC makesthermal contact with a cold pad 124, either by a joining operation orduring initial fabrication of the TEC assembly 220, and the cold pad 124is bonded to the PCM module 200. Both the TEC assembly 220 and the PCMmodule 200 are then mounted on a platform 240 for stability. Aphotoemissive device 20 can then be mounted on the thermally conductingpad 124.

Another method of forming PCM modules is shown in FIGS. 11A-11E. Aperforated foil 310 is placed atop a base foil 320 and bonded, formingwells 315. A phase change material 330 is added to the wells 315. It maybe advantageous to fill the wells under vacuum to avoid the introductionof air. After the wells 315 have been filled they are covered by a topfoil 340. The three foil layers 310, 320, and 340 are bonded together,sealing the phase change material 330 inside the PCM module 300.

Thermoelectrics, Generally

While embodiments of the present invention are not limited to anyparticular thermoelectric module or device configuration, certainillustrative configurations will be understood in the context ofadvanced thin-film thermoelectrics. Accordingly, merely for purposes ofadditional description and without limitation on the broad range ofthermoelectric configurations that fall within the scope of any claimherein that recites a thermoelectric, thermoelectric element,thermoelectric device, thermoelectric structure, thermoelectric couple,thermoelectric module or the like, applicants hereby incorporate hereinby reference the disclosure of commonly-owned U.S. patent applicationSer. No. ______, entitled “LATERAL THERMOELECTRIC DEVICE STRUCTURE ANDRELATED APPARATUS,” naming Ghoshal, Ngai, Samavedam and Miner asinventors, and filed on even date herewith.

Phase Change Materials, Generally

While virtually all materials undergo phase changes with temperature,so-called “phase change materials” or PCMs have transition temperaturesin a range useful for a given application. For example, polymers andwaxes that melt between 28° C. and 37° C. that are used in outdoorclothing to help maintain a comfortable temperature for the wearer maybe used in certain exploitations. Pure elements, like gallium, andcompounds, like water, exhibit sharp phase transitions, for example,melting at a precise temperature. Alloys and solutions, however, oftencomplete the phase transition between liquid and solid states over arange of temperatures. An alloy containing 95% by weight of gallium and5% indium begins to melt when heated above 15.7° C., its solidustemperature. As the alloy is heated further, liquid and solid phasescoexist, and their compositions continually change, but the overallcomposition remains constant. When the alloy is heated to 25° C., all ofthe solid phase material has melted and the liquid alloy has a uniformcomposition. Eutectic compositions are alloy compositions whose solidusand liquidus temperatures are the same, so they behave like pureelements and have sharp melting points.

Relevant design properties of PCMs include the transition temperaturerange, the temperature range over which the PCM can be used, the latentheat of the transition, thermal conductivity, and thermal capacity,which is a measure of the energy that can be stored in the material overa given temperature range and which correlates with the material'sdensity. In general, based on the description herein persons of ordinaryskill in the art will be able to select an appropriate PCM for a givenapplication. PCMs are commercially available from a number of sources.Major classes of PCM include waxes, polymers, hydrated salts, and liquidmetals alloys. Table 1 illustrates several examples of PCMs, includingexamples from each major class.

Waxes are used primarily for lower-temperature applications. Waxcompositions have been developed for an almost continuous distributionof transition temperatures. They typically have low densities andtherefore low thermal capacities, but their light weight can be usefulfor some applications. Thermal conductivities are also low for waxes.Polymers typically exhibit poor thermal conductivity and low latentheats, but they are relatively easy to form and are compatible with manycontainment materials. Hydrated salts are more appropriate than waxesfor higher temperature applications, but they, too, have low thermalconductivities. These inorganic salts are relatively inexpensive and areoften used, for example, in first aid cold and hot packs.

Metals and alloys can be used at temperatures ranging from about −39°C., the melting point of mercury, to well over 200° C. Gallium melts atjust under 30° C., the approximate operating temperature for manyelectronic devices. Metal PCMs typically have high thermalconductivities and large latent heats of fusion. In general, they aremany times denser than other classes of PCM, contributing to higher heatstorage capacities. Some alloys that are otherwise useful as PCMscontain elements that are not environmentally attractive, such ascadmium and lead. Nonetheless these alloys and even elemental Mercurymay be suitable for some applications. In general, Gallium Indium alloyssuch as those illustrated in Table 1 provide an attractive combinationof melt points, high thermal conductivities and large latent heats offusion. TABLE 1 Transition Temperature Composition liquidus solidusDensity (% by mass) (° C.) (° C.) (g/cm³) Class Hg −38.8^(†)  5.43metallic 100 element Ga/In/Sn −7 metal 70/20/10 alloy Paraffin 5 7 0.86wax ClimSel C 7 7 1.42 hydrated salt Ga/In/Sn/Zn 7.6 6.5 6.5 metal61/25/13/1 alloy Ga/In/Sn 10.7* 10.7* 6.5 metal 62.5/21.5/16 alloy(eutectic) Ga/In 15.7* 15.7* 6.35 metal 75.5/24.5 alloy (eutectic)ClimSel C 24 24 1.48 hydrated salt Paraffin 26 25 0.88 wax Ga/In 25 15.76.15 metal 95/5 alloy Ethylene/Vinyl Acetate 27 47 copolymer 60/40 Ga29.8^(†) 5.9 metallic 100 element ClimSel C 32 32 1.45 hydrated saltEthylene/Vinyl Acetate 41 63 copolymer 68/32 Bi/Pb/In/Sn/Cd/Hg 43 389.28 metal 42.91/21.7/18.3/7.97/5/4 alloy Bi/Pb/In/Sn/Cd 47*  47*  9.16metal 44.7/22.6/19.1/8.3/5 alloy (eutectic) ClimSel C 48 48 1.36hydrated salt*Eutectic compositions exhibit equal liquidus and solidus temperatures.^(†)The transition temperature is the melting point of the element.

Generally, any of a variety of phase change materials may be employed inconjunction with the structures and configurations described herein.However, for at least some of the configurations illustrated herein,metals and metal alloys offer an attractive combination of propertiesand compatibilities with materials, temperatures and/or processtechnologies that may be employed in the forming, packaging and/orassembly of illustrated configurations. In general, phase changematerials with phase transition points at or above an expected ambienttemperature will be suitable for thermal moderation and forthermoelectric configurations that employ a body of the material at hot-or cooled-end of a thermoelectric. Phase change materials withtransition points at or below an expected ambient temperature willgenerally be suitable for thermoelectric configurations that pre-chill abody of the material at a cooled-end of a thermoelectric.

In some realizations, a body of phase change material may includeadditional materials introduced to provide nucleation sites during phasetransitions. In some realizations, a body of phase change material maycompressible material or structures (e.g., small polystyrene balls orthe like) to relieve stresses associated with expansion and contractionof the phase change material during phase transitions.

OTHER EMBODIMENTS

While the invention(s) is(are) described with reference to variousimplementations and exploitations, it will be understood that theseembodiments are illustrative and that the scope of the invention(s) isnot limited to them. Many variations, modifications, additions, andimprovements are possible. For example, while a variety of packagingconfigurations have been illustrated, exploitations of the presentinvention(s) need not correspond to any particular illustrated packagingof emissive, sensor or thermoelectric device. In general, packaging andother aspects of physical configuration are matters of design choice andmay be conformed to application, commercially available device and/ormarket constraints as appropriate.

Plural instances may be provided for components, operations orstructures described herein as a single instance. Finally, boundariesbetween various components and particular operations are illustrated inthe context of specific illustrative configurations. Other allocationsof functionality are envisioned and may fall within the scope of theinvention(s). In general, structures and functionality presented asseparate components in the exemplary configurations may be implementedas a combined structure or component. Similarly, structures andfunctionality presented as a single component may be implemented asseparate components. These and other variations, modifications,additions, and improvements may fall within the scope of theinvention(s).

1. An apparatus comprising: an optoelectronic device; a thermoelectriccooler thermally coupled to the optoelectronic device to at leastpartially define a heat transfer path from the optoelectronic device;and a phase change material disposed in the heat transfer path toundergo a transition from a first phase to a second phase thereof andthereby absorb heat transferred by the heat transfer path.
 2. Theapparatus of claim 1, wherein the optoelectronic device is transientlyoperable and wherein the phase change material undergoing the transitionabsorbs a substantial portion of heat evolved by the optoelectronicdevice coincident with such transient operation.
 3. The apparatus ofclaim 2, wherein the thermoelectric cooler is operable to transfer tothe phase change material the heat evolved by the optoelectronic device.4. The apparatus of claim 2, wherein the thermoelectric cooler isoperable to transfer heat from the phase change material.
 5. Theapparatus of claim 1, wherein the thermoelectric cooler is operable totransfer heat from the phase change material and thereby cause the phasechange material to transition from the second phase thereof to the firstphase thereof.
 6. The apparatus of claim 5, wherein the second phase tofirst phase transition is performed prior to or in anticipation of atransient operation of the optoelectronic device.
 7. The apparatus ofclaim 5, wherein the second phase to first phase transition is performedafter a transient operation of the optoelectronic device, therebyreversing a prior first phase to second phase transition of the phasechange material, which absorbed heat transferred across thethermoelectric cooler coincident with such transient operation.
 8. Theapparatus of claim 1, wherein the thermoelectric cooler is transientlyoperable and wherein the transition of the phase change material absorbsa substantial portion of heat transferred across the thermoelectriccooler coincident with such transient operation.
 9. The apparatus ofclaim 8, wherein the optoelectronic device is a sensor device, andwherein the thermoelectric cooler is transiently operable to cool theoptoelectronic device below an ambient temperature.
 10. The apparatus ofclaim 9, wherein the sensor device includes one or more of: a chargecoupled device (CCD); and a complementary metal oxide semiconductor(CMOS) array.
 11. The apparatus of claim 8, wherein the optoelectronicdevice is an emissive device, and wherein the heat transferred acrossthe thermoelectric cooler includes that evolved by operation of theemissive device.
 12. The apparatus of claim 9, wherein the emissivedevice includes one or more of: a light emitting diode (LED); and asemiconductor laser.
 13. The apparatus of claim 8, wherein theoptoelectronic device is transiently operable is substantial synchronywith the thermoelectric cooler.
 14. The apparatus of claim 1, whereinthe thermoelectric cooler is operable to transfer heat from the phasechange material and thereby reverse the first to second phasetransition.
 15. The apparatus of claim 1, wherein the thermoelectriccooler is thermally coupled between the optoelectronic device and thephase change material.
 16. The apparatus of claim 15, whereintemperature of a phase change material facing side of the thermoelectriccooler is substantially clamped based on a latent heat of transformationfor the phase change material.
 17. The apparatus of claim 16, whereinthe clamped temperature corresponds to a first to second phasetransition temperature for the phase change material.
 18. The apparatusof claim 15, wherein the optoelectronic device evolves, duringoperation, a substantial portion of the heat absorbed in the first tosecond phase transition.
 19. The apparatus of claim 15, wherein thethermoelectric cooler transfers, during operation, a substantial portionof the heat absorbed in the first to second phase transition.
 20. Theapparatus of claim 19, wherein the optoelectronic device evolves, duringoperation, a substantial portion of the heat transferred by thethermoelectric cooler and absorbed in the first to second phasetransition.
 21. The apparatus of claim 19, wherein the optoelectronicdevice is cooled, by operation of the thermoelectric cooler, below anambient temperature.
 22. The apparatus of claim 1, wherein the phasechange material is thermally coupled between the optoelectronic deviceand the thermoelectric cooler.
 23. The apparatus of claim 22, wherein,during a heat-evolving transient operation of the optoelectronic device,temperature of the optoelectronic device is substantially moderatedbased on a latent heat of transformation for the phase change material.24. The apparatus of claim 22, wherein the thermoelectric cooler isoperable to transfer heat from the phase change material and therebyreverse the first to second phase transition.
 25. The apparatus of claim22, wherein the thermoelectric cooler is operable to transfer heat fromthe phase change material and thereby transition a substantial portionof the phase change material from the second phase to the first phasethereof prior to or in anticipation of a transient operation of theoptoelectronic device.
 26. The apparatus of claim 1, wherein at ambientconditions, the phase change material is in the first phase thereof. 27.The apparatus of claim 1, wherein at ambient conditions, the phasechange material is in the second phase thereof.
 28. The apparatus ofclaim 1, wherein the first phase is a solid phase, and wherein thesecond phase is a liquid phase.
 29. The apparatus of claim 1, whereinthe first phase is a liquid phase, and wherein the second phase is a gasphase.
 30. The apparatus of claim 1, wherein the first phase is a solidphase, and wherein the second phase is a gas phase.
 31. The apparatus ofclaim 1, wherein the first and second phases are both solid statephases.
 32. The apparatus of claim 1, further comprising: confinementfor the phase change material when in a non-solid state.
 33. Theapparatus of claim 32, wherein the confinement encapsulates the phasechange material.
 34. The apparatus of claim 32, wherein the confinementoperates to inhibit flow of the phase change material when in a liquidstate in part by surface tension of the liquid state phase changematerial.
 35. An apparatus comprising: an optoelectronic device; and aphase change material thermally proximate to the optoelectronic deviceto undergo a transition from a first phase to a second phase thereof andthereby absorb at least a substantial portion of heat evolved bytransient operation of the optoelectronic device.
 36. The apparatus ofclaim 35, further comprising: a thermoelectric cooler operable totransfer heat from the phase change material and thereby reverse thefirst to second phase transition
 37. The apparatus of claim 35, furthercomprising: a thermoelectric cooler operable to transfer heat from thephase change material and thereby transition a substantial portion ofthe phase change material from the second phase to the first phasethereof prior to or in anticipation of the transient operation of theoptoelectronic device
 38. A method of moderating temperature of anoptoelectronic system, the method comprising: transiently operating anoptoelectronic device that evolves heat; and absorbing at least asubstantial portion of the heat evolved by transient operation of theoptoelectronic device in a phase change material thermally proximate tothe optoelectronic device, the phase change material undergoing atransition from a first phase to a second phase thereof.
 39. The methodof claim 38, further comprising: transferring heat from the phase changematerial and thereby reversing the first to second phase transition. 40.A method of cooling an optoelectronic device, the method comprising:transferring heat from the optoelectronic device along a heat transferpath that includes a thermoelectric cooler; and absorbing, in a phasechange material undergoing a transition from a first phase to a secondphase thereof, at least a substantial portion of the heat transferred inthe heat transfer path.
 41. The method of claim 40, further comprising:transiently operating the optoelectronic device and thereby evolving asubstantial portion of the heat transferred and absorbed in the phasechange material.
 42. The method of claim 41, further comprising:transferring to the phase change material, using the thermoelectriccooler, the heat evolved by the optoelectronic device.
 43. The method ofclaim 41, further comprising: transferring heat from the phase changematerial, using the thermoelectric cooler.
 44. The method of claim 40,further comprising: transiently operating the thermoelectric cooler totransfer thereacross a substantial portion of the heat absorbed in thephase change material.
 45. The method of claim 44, further comprising:transiently operating the optoelectronic device in substantial synchronywith the thermoelectric cooler.
 46. The method of claim 40, furthercomprising: transferring heat from the phase change material, using thethermoelectric cooler, thereby reverse the first to second phasetransition.